Paper press roll assemblies



1955 E. J. JUSTUS 3,198,697

PAPER PRESS ROLL ASSEMBLIES Filed June 26, 1964 5 Sheets-Sheet 1 I N VEN TOR.

Edy zf d ad 215' BY t ATTORNEYS g- 3, 1965 E. J. JUSTUS 3,198,697

PAPER PRESS ROLL ASSEMBLIES Filed June 26, 1964 5 Sheets-Sheet 2 I N VEN TOR.

ZZc Z YB 5% 2 ATTOR E YS Aug. 3, 1965 E. J. JUSTUS 3,198,697

PAPER PRESS ROLL ASSEMBLIES Filed June 26, 1964 5 Sheets-Sheet 3 INVENTOR.

Faya/ a] My? ATTORNEYS 3, 1965 E. J. JUSTUS 3,198,697

PAPER PRESS ROLL ASSEMBLIES Filed June 26, 1964 5 Sheets-Sheet 4 x-m-A -/o i IINVENTOR.

Zafgaf ([JZZQZZZ BY WM z 'ag %4/A ATTORNEYS Aug. 3, 1965 E. J. JUSTUS PAPER PRESS ROLL ASSEMBLIES INVENTOR. la? 57 ifilllf 5 Sheets-Sheet 5 ATTORNEYS Q\ lllm Filed June 26, 1964 United States Patent 3,18,697 PAPER PRESS RQLL ASSEMBLIES Edgar J. Justus, Beloit, Wis, assignor to Beloit (Porpcration, Beloit, Win, a corporation of Wisconsin Filed June 26, 1964, Ser. No. 378,217 11 Claims. ((31. 162-372) The present invention relates to an improvement in devices for dewatering felts, paper Webs, etc. and more particularly to improvements in press roll shells for the dewatering of paper webs and felts in paper making machines.

uAlthough the instant invention may have other uses and may involve the use of devices somewhat different from those described herein, it will be appreciated that an understanding of the instant invention involves a descripfion of a paper machine press section comprising a number of different press nips, showing embodiments of the various devices hereof, which have certain common principles, even though there are also differences among these devices. An important feature of the instant invention is that it provides an inexpensive grooved press roll shell structure, heretofore unknown, in that the grooves afford freedom of water movement through a felt in a paper machine while simultaneously avoiding the shadow marking effect generally characteristic of all press roll shells having water receiving recesses therein.

In general, certain corrugated partially dried paper pulp materials and other very crude paper board materials have been made or at least the making thereof has been suggested by prior workers proposing the use of grooved roll-s which will thus subject the paper .web to ultimate areas of high and low pressure for purposes of dewatering. These various grooved rolls, however, have all been quite crude in nature and were long since discarded, if they were ever used commercially to any significant extent; and since the early 1920s at least suction rolls have been employed as the principal type of press roll for the dewatering of webs. In a suction roll, the web is pressed against a solid surface on one side (eg. a plain roll) and it .is pressed against this solid surface by a felt or belt of water permeable, usually compressible absorbent material. The felt itself is pressed against the web by a solid surface containing a number of perforations therein, at which subatmospheric pressure is maintained. These are the perforations of the suction roll. In this arrangement the land areas of suction roll provide rigid solid surfaces for applying pressure against the felt protecting the web and the underside 0r backside of this felt is also exposed to localized regions of subatrnospheric pressure inbetween such land areas, for drawing of the expressed water from the web to the felt and into such subatmospheric pressure areas and connected glands.

In spite of the excellence of performance of many suction rolls and the essential nature of their use in certain types of paper machines, it must be appreciated that they are expensive to install and in some instances comparatively expensive to operate, because of maintenance of subatmospheric pressure within the suction gland and other with more routine maintenance problems.

The essence of the suction press nip, however, does involve an actual removal of water from not only the web but the felt covering the subatrnospheric pressure locallzed areas or perforations, and this water is withdrawn from the felt-web system at the suction press nip.

In recent times, a different principle has been employed in the dewatering of paper webs. The suction press nip, as previously mentioned, does actually withdraw water from the web-felt system at the nip, but this water is withdrawn at subatmospheric pressure areas which are localized but which are of relatively large size (eg. A: to

Mi inch diameters) and this creates a situation wherein the web travelling through the nip has localized areas that are subjected to the maximum nip pressure opposite land areas on the perforated suction roll shell and other localized areas that are not subject to this maximum pressure and are, instead, subject to a substantially lower pressure, in view of the subatmospheric pressure at the backside of the felt in such localized areas (opposite the perforations in the shell). This creation of marked pressure differentials at the nip area may in many instances cause what is known as shadow marking in the web. This is true even though the perforate suction roll shell is ordinarily employed in press nips involving maximum pressure of perhaps only 200 or 300 pounds per lineal inch in the cross machine direction. In the case of nips having a nominal peripheral dimension, it will be appreciated that the pressure per square inch in the region of the land areas applied directly against the underside of the felt may be substantially greater than the pressure in pounds per lineal inch, whereas the application of a suba-tmosphen'c pressure at the localized regions opposite the suction roll perforations will thus create a pressure differential between .the land and perforate areas of the nip of substantial magnitude.

In more recent work, however, it has been found that by use of a different principle the perforate suction roll type of press nip may be avoided in certain locations in the paper machine. This comparatively new principle involves the use of the socalled divided press, wherein the web is pressed against a comparatively drier felt, between substantially plain roll surfaces, so that the only significant water movement involves movement of the water from the web to the felt, and the web and felt are then separated at the offrunning side of the web press nip in such divided press and the felt is subsequently treated in a separate felt only press where it is dewatered, cleaned and reconditioned for reentry into the web press. The dewatering, cleaning and conditioning of the felt at the felt only press may involve the use of suction rolls or various other devices which can and often do apply nonuniform pressures across the nip load line for purposes of dewatering, but the use of such non-uniform pressure application to .the felt alone does not really cause any particular permanent change in the felt structure (except perhaps increased wear) so that the felt returning to the Web nip does not impart any sort of shadow marking to the web as a consequence of the treatment in the felt only mp.

In the divided press, one problem had to be faced, however, because often the water loads are rather substantial. This problem involves crushing, which is a term applied by paper makers that is perhaps a misnomer, but which has very great significance in the art of paper making in that it is the term applied by paper makers to indicate what is evidenced as incipient fractures or cracks in the final web product. Crushing is elfected by undesirable and/or excessive water flow in the region of press nlps, generally speaking in the plane of the web, so as to cause disruption in the web itself, the desired interlocking of the fibers in the web, etc. i

In a so-called divided press, crushing has been recognized as a problem and certain solutions have been offered. For example, United States Patent No. 3,023,805 issued to Walker and assigned to the assignee of the in stant application provides one type of solution in that it provides a press roll having an imperforate shell with a blind drilled rubber cover thereon for at least temporarily receiving the water expressed from the web and through the felt at the web nip. 'It will be appreciated that these blind drilled holes are extremely fine in size and the water of the nip (over and beyond that which the felt itself may receive and retain) passes through the felt'and into these .minute holes or perforations in the rubber cover. Often, the water driven into these minute blind holes will entrap air therein and build up a back pressure therein, and to some extent this is not undesirable for the reason that it creates a somewhat better pressure balance at the nip, in that the perforations thus receive water but they retain water under a certain amount of pressure so that the felt exposed to these perforations at its back side does not have the greatly reduced backside pressure (compared with the pressure applied at land areas) that is characteristic of the use of perforate suction roll shells. In fact, the blind drilled holes form a myraid of very minute perforations that are generally smaller in area than the suction roll perforations and this fact, coupled with the tendency of the creation of a back pressure or at least the avoidance of a subatrnospheric pressure on the backside of the felt opposite such perforations does afford a better pressure balance and the web itself passing through the nip is not subjected to localized substantial pressure differences of the type characteristic of the suction roll operation. In general, these blind drilled holes minimize but they do not completely avoid any tendency toward shadow marking and theyare thus an improvement over the conventional perforate suction roll. In this particular respect, even though it must be appreciated that the divided press assembly of the type just described has certain limitations in connection with the total amount of water removed which generally makes such divided press incapable of removing the substantial amount of water that may be removed at suction presses, even at reduced nip loads in pounds per lineal inch. The divided presses, 'however, may be employed at substantially greater nip pressures or loads in pounds per lineal inch and, because the blind drilled holes on the rubber cover are supported by a generally imperforate continuous shell, anti-deflection means and the like may be used to considerable advantage in obtaining relatively uniform nip pressures across the full width of the machine, so that higher nip pressures may 'be used and they may be used with satisfactory operation.

The essence of the divided press principle, however, is that the rolls at the web press nip do not themselves actually effect any permanent removal of water .from the web and felt system passing through the nip. Instead, there is only a temporary forcing of what otherwise would be overloading quantities of water into the blind drilled holes of the press hip and at the immediate offrunning side of the press nip the highly absorbent felt will expand, not only creating a partial vacuum or subatmospheric pressure within the body of the felt itself, but also receiving water under pressure very rapidly from the blind drilled holes (particularly in cases when the water in the blind drilled holes has entrapped and compressed air at the bottom of the blind drillings). Thus, the basic concept involves the use of devices such as blind drilled holes and the divided press which will tend to avoid the shadow marking problem in a favorable way, but which do not actually effect water removal from the overall felt and web system at the web nip. Instead, the felt and web must be separated as rapidly as is practicable at the offrunning side of the web nip so that the highly absorbent felt may receive water from the blind drilled holes of the press roll without, in turn, significantly rewetting the web at the offrunning side. The felt is introduced into the web press (in the divided press) in a relatively dry condition of approrimately 65% dry, for example in the case of woolen felts, so that it is readily capable of not only receiving but retaining a certain significant quantity of water from the web, but this felt must then be separated immediately from the web at the offru-nning side and passed through the felt only nip in order toeffect the es sential dewater-ing of the felt to recondition the same for return to the web nip. Thus, the water is removed permanently from this particular system not at the web press, but rather at the felt only press. Again, it must be appreciated that both the suction roll presses as well as the divided press systems have unusually superior uses in certain arrangements and they are capable of excellent performance.

The instant invention, however, contemplates the use of still another entirely different principle of water removal which afford-s advantages over both the suction press nip and the divided press assemblies in one respect to another. In addition, the instant method is versatile to the extent that it may be used for dewatering webs in conjunction with divided press systems and/ or suction press systems.

Briefly, the instant invention contemplates a concept of dewatering the web at a web nip (and/ or the felt alone at a felt only divided press nip) in which water is actually permanently removed from the web felt system, by the application of pressure to the underside of a felt (pressing the web against a solid surface) along a plurality of very closely spaced local areas which are substantially coextensive with the felt at the pressing area to the extent that as much as about /3 or preferably as much as or /s of the backside of the felt is pressed against the web by solid surfaces, between which relatively minute extremely narrow regions of the backside of the felt are exposed substantially to ambient atmospheric pressure. In the instant arrangement, these regions are so very narrow in width, that the venting of the backside of the felt in these very limited regions does not result in any significant reduction in the pressure applied to the web on the working face of the felt opposite such vented localized areas. This is because the localized vented areas are so narrow that the felt of ordinary weave in structure is capable of bridging the same between the land areas which are applying pressure to such an extent that a substantially uniform pressure is applied to the web across the full width of the so-called nip load line, even though the very narrow localized vented areas on the backside of the felt readily receive water expressed from the web and through the felt and carry the same away from the web-felt system being pressed. In addition, at the instant that pressure is removed from this system, it will be appreciated that the highly absorbent and relatively compressible felt will expand immediately tending to create a partial vacuum or subatmospheric pressure within the body of the felt. The compressed web on one side of the felt will not afford much of an opportunity for ambient atmosphere to enter the felt from this side so as to satisfy this partial vacuum, so ambient atmosphere \and/ or water vapor and/ or water itself must enter the backside of the felt in this particular region in order to satisfy the partial pressure created within the body of the felt. In the practice of the instant invention, it will .be appreciated that the felt is thus temporarily exposed in this subatmospheric pressure condition to substantial (water-free for practical purposes) land areas which have been applying pressure to the felt, as well as extremely small or narrow grooved) vent areas which had received water from the felt which may have contained a certain amount of water. These vent areas are, however, such a relatively small amount of the total area exposed to the underside of the expanding felt and they are so narrow that the side walls thereof tend to resist the movement of water back into the felt at the underside thereof. Thus, with sumciently rapid movement of the felt away from such vente pressing surfaces, the felt may carry its internal partial vacuum out into ambient atmosphere, at which time the partial vacuum is readily satisfied by air, rather than the re-entrance of water into the expanding felt. Other specific aspects of the instant invention will be described in greater detail hereinafter.

It is, therefore, an important object of the instant invention to provide an improved press roll shell for dewatering felts, paper webs, and the like.

Another important object of the instant invention is to provide an improved grooved press roll shell for dewatering paper webs by the use of dewatering means which effect removal of water from a paper web and a felt carrying the same, without undesirable shadow marking, crushing, or the like web damage.

Other and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure thereof in the drawings attached hereto and made a part hereof.

On the drawings:

FIGURE 1 is an essentially diagrammatic side elevational view of a press mechanism employing the methods of the instant invention;

FIGURE 1A is a fragmentary detail view taken substantially along the line AA of FIGURE 1;

FIGURE 2 is a fragmentary detail sectional view showing a portion of a suction press nip of the prior art;

FIGURE 3 is a view comparable to FIGURE 2 showing a portion of a press nip embodying blind drilled holes in a roll, used in the prior art;

FIGURE 4 is a view comparable to FIGURES 2 and 3, but showing a portion of a press nip designated N-6 in FIGURE 1 (in sectional elevation);

FIGURE 4A is a view of a fragmentary detail cross machine section taken substantially along the line AA of FIGURE 4;

FIGURE 5 is a view comparable to FIGURE 4, but taken'substantially along the line VV of FIGURE 1;

FIGURE 5A is a view comparable to FIGURES 4A and 5 but taken substantially along the line VA-VA of FIGURE 1;

FIGURE 5B is a fragmentary sectional elevational view that is generally an enlargement taken substantially from the encircled portion designated VB in FIGURES 5 and 5A, but with section lines omitted for ease in reference to the various dimensions and other specific critical features thereof shown in the drawing of FIGURE 5B;

FIGURE 5C is still another view comparable to FIG- URES 4A, 5 and 5A, but taken substantially along the line VCVC of FIGURE 1;

FIGURE 6 is an essentially diagrammatic elevation of an enlargement of a press assembly shown in FIGURE 1 and designated by the reference numeral 20; V

FIGURES 7 and 7A are fragmentary sectional detail elevational views taken substantially from the encircled areas designated VIIVII and VIIA-VIIA of FIG- URE 6;-

FIGURE 8 is an enlarged press assembly showing another embodiment of the invention;

FIGURE 9 is a fragmentary top plan view of another grooved press roll design concept the use of which involves certain principles of the invention;

FIGURES 9A, 9B and 9C are essentially fragmentary detail views taken, respectively, along the lines IXA-- IXA, IXB-IXB and IXCIXC of FIGURE 9;

FIGURES .10 and 11 are essentially diagrammatic side elevational views of other press assemblies involved in the practice of the instant invention.

As shown on the drawings:

In order to appreciate the fundamental concepts hereof, a press section employing the same must first be studied. Referring to FIGURE 1, it will be seen that a press assembly is indicated generally by the reference numeral 10 wherein the web W-l is picked up by a suction pickup elt 11 and passed through an initial nip- N-l (between a pair of felts 11 and 52) defined by press rolls 12 and 14. The web W-'1 then follows the pickup felt 11 around an appropriate guide roll 11b and into a second web press nip N-2 defined by rolls 47 and 48, from which the web W1 drops onto a press felt 23 and is carried into a third web press nip N-3 defined by the rolls 2'1 and 22 and the web W-l may continue onto the dryers or it may be subsequently further subjected to mechanical pressure.

In essence, in the elevation '10 here shown, it will be seen that the suction pickup felt 1'1 carries out several functions. First of all, the felt 11 is mounted on a numher of conventional felt guide and stretching rolls, desig-' nated 11a through 11k, and this felt 11 passes around a suction pickup roll l) where .it picks up the web W-l from a wire reach between a conventional suction couch roll 8 and the related turning roll 8a.

The felt 11 then guides the web W-l down onto a second felt 52 and the web W-1 sandwiched between these two felts 11 and 52 passes through the first press nip N-I which is a generallyvertical press nip defined between two generally horizontally aligned press rolls 12 and 14. The press roll 14 is within the loop of the felt 11 and a fragmentary view of the grooved surface of the press roll 14 is indicated in FIGURE 5C and will be dis-. The roll 12 (which cussed in greater detail hereinafter. is within the loop of the other felt 52) is also a grooved roll and the general construction of the working surface of the grooved roll 12 is also indicated in FIGURE 5C.

As previously indicated, the felt I1 is so constructed as to cause the web W-l to follow it out of the nip N-l; and this is done by using a closer weave in the felt 11 in the manner well known in the art. The felt 11 then carries the web through a second press nip N-2 as indicated being defined by the rolls 4-7 and 48. The roll 47 is within the loop and as will be explained in some detail. hereinafter, the roll 47 may and preferably is also a' grooved roll having substantially the structure of the roll 14 which will be described in detail hereinafter. At the oif'running side of the nip N-Z a save all pan 1100 is operated in association with the guide r-oll 11a. The felt 11 then passes upwardly to a felt only press nip N-fi which is defined by a plain press r-oll 12a and a grooved roll 13, with the grooved roll 13 being on the outside of the loop of the felt 11 and being shown in somewhat greater detail;

in FIGURES 4, 4A and 4B. The felt is thus reconditioned for its return back to the suction pickup roll 9.

Referring to the second felt 52, it will be seen that this felt also passes through the nip N1 in contact with the web W-l and passes around appropriate felt guide and tensioning rolls shown generally at 52a through 52a. The felt 52 is also part of a divided press arrangement in that it picks up water from the web W-l at the nip N-l and is subjected to a separate felt only treatment at a nip N-7 defined by a plain roll 21y within the loop of the felt 52 and a grooved roll 22y outside the loop of the felt 52. The

grooved roll 22y is substantially identical in structure to the previously described grooved roll 22 (and this structure may be referred to hereinafter as the roll 22 structure) and the rolls 22y and/ or 22 are shown in greater detail in FIGURES 5A and 5B, but it will be noted that the grooved roll shown in FIGURE 5B (and designated 22) actually has substantially the preferred structure of the grooved rolls designated in FIGURE 1 as 12, 14 and 22;

and it will be further pointed out in this discussion that,

oncoming side of the nip N-4. Corresponding wiping devices w and doctors d as well as saveall-s 22h, 12h, 14h, 47h, and 13h, respectively, are shown for the various rolls.

Grooved rolls in the art of pressing paper webs were.

considered and discarded several generations ago. For example, in 1915, US. Patent No. 1,123,388 issued to Schaanning and was directed to a grooved press roll allegedly intended to replace felt covered rolls and having grooves of such configuration that Schaanning alleged that they would retain water by capillary action. As early as 1905, Fletcher (US. Patent No. 800,845) proposed a grooved roll made of certain segmental portions. In the 1920s, Goodfellow (US. Patent No. 1,369,355) proposed a press roll with circumferential grooves of unspecified size as well as generally axial grooves of unspecified size interrupting the circumferential continuity of land areas,

which were covered with the felt; and Wagner issued U.S. Patent No. 1,483,562 relating to grooved rolls used with a pair of press felts for cooperation with certain suct1on mechanism outside of the press rolls. Wagner U.S. Patent No. 1,321,956 shows grooved rollers in a couching mechanism. Wagner U.S. Patent No. 1,520,489 relates to a grooved jacketed roll. Wagner U.S. Patent No. 1,517,036 relates to a pair of press rollers intended to press a traveling paper web with their bare unprotected surfaces, with one of such rollers having grooves in the surface thereof. Wagner U.S. Patent No. 1,552,098 shows very shallow as well as narrow grooves intended to dewater pulp entering the same.

As late as 1958, however, Wagner issued US. Patent No. 2,858,747 which was directed to grooved press rolls functioning with a suction device mounted outside of the roll shell; but with occasional exceptions such as this in the patent art, it will be found that substantially the entire paper making industry devoted its attention to the perforate shell type of suction roll for water removal at a press nip, once this structure was discovered and introduced in the industry. In fact, for the past thirty or forty years the drilled perforate shell type suction roll has been used predominantly and practically exclusively in the paper making industry for the removal of water in any significant quantities from moist paper webs in paper making machine press assemblies.

As indicated in FIGURE 2 hereof, in the suction press nip N 4, the roll shell 31 is perforate, being provided with a multiplicity of holes 32, 32 of substantial size (i.e. at least about inch in diameter and usually having flared peripheral mouths 32a of greater size) which are drilled entirely through the roll shell 21 (having at least about 1 inch thickness) to communicate with the suction gland G extending the full width of the roll shell 31 interiorly opposite the nip N4. At the suction press nip N-4, a press felt 33 is interposed between the web W-2 and the perforate suction roll shell 31 (primarily as a Water-permeable protective layer for the web W2), and water expressed from the web W-2 passes completely through the felt 33 and into these holes 32, 32 in the perforate shell 31. Some water continues into the gland G and some is usually retained in these holes 32, 32 at the elf-running side of the nip N.4, where the subatmospheric pressure in the gland G tends to counteract centrifugal forces urging water droplets back out of the holes 32, 32'and against the felt 33 under ambient atmospheric pressure. The felt 33 may thus remain in contact with the Web W2 at such off-running side of the nip N4 without substantial rewetting of the web W-Z (via Water thrown back on the felt 33 from the suction roll holes 32, 32). Also, savealls (not shown) are conventionally positioned between the felt 33 and the perforate roll shell 31 at the immediate off-running side of the gland G to catch droplets released from the suction roll holes 32, 32, particularly after these holes pass beyond the limit (i.e., the off-running seal, not shown) of the interior suction gland G so there is no longer a pressure differential holding the droplets in the holes 32, 32. The off-running felt 31 must be guided to avoid such saveall and this often results in guiding the felt with or against the web at the off-running side of the nip N-4. The perforate suction roll with its suction gland, and with or without the saveall, thus functions to carry away substantially all of the water expressed from the web at the nip.

In spite of the excellence of the performance of perforate suction rolls for a number of uses in paper making, it must be conceded that these rolls and their auxiliary equipment are expensive to manufacture. The suction gland therein, also, substantially precludes the use of conventional anti-deflection roll structures for greater versatility and uniformity in nip pressure control. In addition, the substantial size of the perforation mouths 32, coupled with the pressure differential created by the suction gland against the unsupported portions of the felt 33 opposite 3 such perforations 32, has a tendency to cause shadowmarking of the web in certain instances.

Only in recent times, after many years of commercial use of perforate suction rolls, there has been developed what is known as the divided press type of structure which does not require the use of the perforate suction roll at the web press. In the divided press, the felt alone is cleaned, dewatered and conditioned at a separate press nip, and then fed with the moist Web into what is called a Web nip which is defined between rolls having imperferate shells (as contrasted to the perforate suction roll shells). As indicated in FIGURE 3, ordinarily the amount of water load at such a web nip N-S is such that at least one of the press rolls 35, 35a is provided with recesses 36 on the surface thereof to temporarily take the load of water entering the Web nip N-S to prevent crushing of the web W-3 carried by the felt 37. As indicated in FIGURE 3, a preferred form of such recess 36 is provided by a rubber cover on a press roll 35 that contains a myriad of comparatively fine blind drilled holes (i.e. of approximately to 4 inch or even less diameter, as in the case of Walker U.S. Patent No. 3,023,805); and such fine holes 36, 36 will in the case of most conventional webs W-3 and felts 37 substantially avoid or eliminate the shadow marking characteristic of the performance of certain perforate suction rolls. In the divided press, the water removal principle is substantially different. The water is not carried away from the nip N-4 by the suction roll shell 31 and, instead, the water pressed from the web W-3 into the felt 37 is carried away from the web W-3 substantially entirely by the felt 37 at the off-running side of the nip N-S. Excess water at the nip N-S which is driven into the blind hole perforations 36, 36 to relieve the load at the nip N-S, ordinarily entraps a certain amount of air in the bottom of these blind perforations 36, 36 and this, coupled with the ability of the felt to absorb water when itexpands at the off-running side of the nip N-S, results in a substantial removal of water from the system via the felt 37 which, as previously mentioned, is then passed through a felt only press where it is dewatered to the extent desired at a separate press nip. The principle of the water removal at the web press nip N-S of the divided press also involves what amounts to a comparatively good force balance at the nip itself, whereat the web W-3 is squeezed so that it is dewatered but it is squeezed against a felt 37 that is maintained on a substantial amount of land area 36a in between the mouths of the myriad of perforations 36, 36 and the perforations 36, 36 are filled with water under a considerable amount of pressure (particularly when air is entrapped in the bottom of the blind holes 36, 36) so that the bridging or unsupported felt areas at the nip N-S corresponding to perforation openings of as much as /8 or A of an inch in diameter are actually very well supported from beneath and there is little significant evidence of lack of support for such felt areas in the resulting pressed web W-3 ordinarily (i.e. little, if any, evidence in the form of shadow marking). In addition, the imperforate shells 35, 35a effectively defining the Web press nip N-S of such construction that they lend themselves readily to support by various anti-deflection means, so that the web press N-S is afforded substantial advantages in versatility of nip pressure control and maintenance of generally uniform axial nip loads.

The instant invention, however, as exemplified in the embodiments of FIGURES 4, 4A and 4B, as well as the improvements thereon represented in FIGURES 5A, 5B and 5C is based upon still another ditferent and distinct fundamental principle of water removal at press nips. For one thing, the instant invention provides a unique improvement in the divided press assembly (FIGURE 1) whereby a grooved roll is used in place of the roll 35 described in connection with FIGURE 3 (or as will be explained hereinafter at the felt only nip) so as to obtain either a number of distinct advantages over the divided web press structure just described (at some sacrifice in other advan- 9 tages), or to obtain all of the advantages of the divided press just described, plus a number of additional advantages.

One of the essential concepts of the instant invention involves that of using a grooved roll with land areas 13b and 22b (of the FIGURE 4 and FIGURE 5 series) that are substantially circumferentially continuous so that the land areas present continuous generally cylindrical, smooth exterior or peripheral outer operating surfaces for engaging the Web material or felt 11 and supporting the same and causing the same to bridge the grooves. Circumferentially discontinuous land areas are substantially impossible to clean during the rotation of the roll. Also essential in a consideration of this first concept is the use of such land areas having a very narrow axial dimension 17, 27 between the alternating grooves 13, 220 which are also of small axial dimension 16, 26 but which are vented (peripherally) to ambient atmosphere so that Water pressed at the pres nips N-l, N2, N-3, N-6 and N7 will have no resistance in this respect to flow through the web material or felt axially as well as radially into the vented groove mouths (which are themselves wide enough to readily receive the water under pressure). The grooves are provided in a size of sufiicient magnitude to receive the Water load at the press nip, while being vented to ambient atmosphere and thus in a manner so as not to resist flow into the grooves, by virtue primarily of the groove depth (as compared to increased groove axial dimensions 16, 26 to accommodate increases in water load). The groove depth 18, 28 in most paper machine uses must thus be substantially greater than the groove opening 16, 26 at the roll periphery, so that the very essential venting function is accommodated. In practical embodiments of the instant invention, the ratio of groove depth 18, 28 to groove axial dimension 16, 26 at the groove periphery is preferably at least about 2:1 and may be as much as 10:1 or more depending upon practical, additional considerations such as roll strength, ease of cutting the grooves, etc. In addition, it has been found important to make sure that the groove is able to readily receive the water load in that it is provided with side walls 13c1, 13c-2 or 22c-1, 22c2 which are (generally radially aligned) at least as far apart axially as the groove mouth 16, 26 for at least an initial groove depth substantially equal to the axial dimensions of 16, 26 of the groove mouth (or a minimum of about 0.05 inch, and preferably inch) and preferably for substantially the entire groove radial dimension 18, 28. It will thus be seen that a minimum groove cross sectional area may be computed as 2x on the basis of the example of 0.025 inch groove width 26" and 0.050 inch groove depth, although a greater area is preferred in the neighborhood of 52: for a depth of 0.125 inch. This concept would permit interior groove axial dimensions greater than the mouth axial dimension 16, 26, if the forming of the same is practical and does not subtract from the strength and other commercial considerations such as cleaning of the roll, but this concept would preclude shallow tapered grooves which would be intended to resist the entrance of water therein (and/ or the venting thereof) but a (conventional cutting machine) taper between the walls of relatively deep grooves, such that the walls would be functionally parallel (for the operating purposes described) in the region of the groove mouths would not be precluded.

In addition to the ability of the grooves 130 and 22c to vent to ambient atmosphere at the press nip and thus readily accommodate the receipt of Water, an even more im portant consideration has now been found to be a part of this concept, and this is the consideration which involves the use of a minimum axial dimension 1'7, 27 to the smooth generally cylindrical land area on the ridges between the grooves. As indicated in FIGURE 53, the maximum axial distance which water must travel through the felt 23 (in compressed form) is from approximately the midpoint M of the land area 22b to the edge of the groove 22c adjacent thereto. Such midpoint M lies in a generally radial plane bisecting the individual ridge and land area 2217 and the axial distance 27 /2 to the groove is approximately /2 of the land area 27 (on the average, even in FIGURE 9).

Liquid per se in any medium, such as water in the web type of medium provided by the felt 23, resists flow under any circumstances, and in the compressed felt 23, which has a dimension within the range of about 5 to Ms inch (0.0625 to 0.125 inch) the resistance to water flow is sufliciently great to cause considerable care to be taken in defining this dimension 27 /2 so as to maintain maximum dewatering efliciency at the nip. (Lightweight felts are often compressed to inch thickness; in such instances the ratio of axial land dimension 17, 27 to felt thickness may be 3:1 to 10:1.) In this respect, the axial land dimension 17, 27 should be about 25% to 200% (i.e. up to about 200% of inch or 0.25 inch) of the radial felt thickness 23a in compression for the best performance in water flow axially laterally through the compressed felt and into the grooves 220 on either side of each land area 22b (that is contacted, touched or, in the language of the art covered or wrapped by the felt 23). The range of axial land dimension 17,27 to felt thickness 23a in compression thus may be 1:5 to 3: 1 but preferably is within 1:2 to 1:1.

Still another important consideration in the practice of the instant invention with respect to the axial groove dimension 16, 26 at the mouth thereof is that of shadow marking in the case of webs passing through the nip. It will be appreciated that shadow marking per 'se is not of any consequence in connection with a felt only press, nor is it a significant factor in the case of certain types of lower quality webs or in the case of certain paper machines wherein extra heavy felts are used. In such instances, it might be possible to use grooves having substantial axial dimensions 16, 26 up to as much as about Ms inch, above which the felt would tend to enter the grooves to too great an extent, causing unnecessary additional wear of the felt, possible plugging of the water flow and/ or venting efiect, etc. A careful study of this matter has revealed, however, that the axial groove dimensions 16, 26 which are significantly greater than about 0.035 inch tend to cause undesirable marking on certain webs and/or the undesirable temporary entrance of the felts of most weights into the grooves under the nip load, so as to increase the wear of the felts; and a maximum groove dimension of 0035 has been found to be a very significant cutoff point for most pressing operations. The minimum practical axial groove dimension 16, 26 which accommodates receipt of water and the essential venting function, is in the neighborhood of about 0.005 inch. As previously indicated excellent results are obtained using a groove axial dimension of substantially 0.025 inch, although more recent work indicates a distinct preference for 0.020 inch (thereby giving preference to 0.02 to 0.025").

The foregoing venting concept which is essential to the practice of the instant invention is based upon certain fundamental theories which involve the design of grooves having the best ability to receive water and vent the nip pressure, plus the design of land areas having superior ability to effect axial or transverse flow of water through the compressed felt and into the grooves with a mini mum amount of interference and a minimum amount of pressure gradient across the land areas. In the case of a Web nip such pressure gradient is a function of the fluid pressure existing at the interface between the felt and the web, and it is important in pressing to vent or relieve such fluid pressure in the felt to as low a level as possible, which is best done by opening up the back side of the felt so that water need travel only substantially the thickness of the felt in compression to ambient atmosphere in the grooves.

FIGURE 6 hereof is exemplary of certain aspects of the invention, showing in greater detail the web press 11 N-3 of FIGURE 1 (with the web W-l thereof being indicated at Wd in FIGURE 6). The compartmented saveall a, 25b, 25c effectively retains water removed at the nip N-S. Some water D-3 is thrown from the surface of the roll 22. More water 29d is pumped from the grooves thereof by the pumping wiper 29 fixed at 2% and extending as an axially and peripherally continuous metal sheet 20a from touching contact at the line L-l gradually away from the roll periphery (lands 22b) as seen in FIGURE 7 to pump water out of the grooves 22c with inrushing air A7. And residual water droplets D (FIG. 7A) are then wiped from the lands 22b (or blown therefrom by an air doctor) by a conventional axially continuous mechanical doctor at the immediate one coming side of the nip N3. The guide rolls 24a and 24b preferably guide the felt 23 above the common tangent plant T-T to minimize contact between the grooved roll 22 and the felt 23 except at the nip load line (which also happens to be the section line indicated at V-V).

Another aspect of the. instant invention which has been found to be very important is that of minimizing such flow of water through the. compressed felt and into such grooves, by preparation of the land areas at the oncoming side of the nip.

It will be appreciated that doctors d (30 of FIG. 6) are shown at the oncoming side of the various grooved roll nips of theinvention and these doctors perform a distinct function in this position. Essentially, of course,

they do not reach into the grooves and they function only to wipe the land areas dry, but in wiping the peripheral land areas dry of all droplets of Water, these doctors d serve to avoid the necessity of water being driven into the felt and then being forced at the nip axially through the felt back into the grooves. These doctors thus function at the oncoming side of the nip to avoid water actually being carried on the roll as well as to remove water deposited on the surface of the roll as mist or otherwise. In general, the doctor should be within 90 of the nip itself, but in certain special situations such as in the case of the doctor for the roll 12, it is not possible for the doctor to be this close to the oncoming side of the nip N-l, but it is positioned within 120-180 of the nip N-1. It will be appreciated that mechanical doctors function very readily for this purpose, but air doctors or other doctoring devices may be used. Essentially they are substantially axially continuous devices functioning in close-running relation or actually pressed against the land areas of the rolls. It will be appreciated that if some of the moisture is wiped from the land areas back into the grooves of the doctor this is not as detrimental as it might appear, because the grooves are designed to be deep enough to accommodate a certain amount of excess Water and still carry out their essential venting function. The important essential function of the doctor is to remove the moisture from the surface of the land area so that it will not have to travel through the compressed felt at the nip into the grooves.

Still another very important point to consider is that the press roll 22 which is the preferred embodiment of the instant invention, is provided with generally circumferential, alternating grooves 220 and ridges 221) which are in the form of continuous but very slow spirais, as contrasted to exactly circumferentially aligned and exactly axially spaced grooves and ridges throughout the entire roll periphery. This latter structure can be used in the practice of the instant invention with a number of desirable results. The spiral grooving is distinctly superior from the point of view of manufacture and use. Machine tools are available for cutting the spiral grooves with considerably greater case than the cutting of exactly circumferential grooves can be accomplished. It Will be appreciated that the spiral angle or the angle of the grooves 22 withthe centroidal axis of the roll shell should be comparatively small. Such small angle, alpha, might be expressed for a 20-inch diameter press roll (i.e. 10-

12 inch radius) as tangent alpha equals approximately 0.125 divided by 10, 0.0125. The range for tangent alpha should be within about 0.003 to about 0.03, preferably.

It will be appreciated that the grooving at this relatively slow spiral has substantially no axial movement relative to the felt which is moving with the roll surface at the nip, so that felt wear is minimized. On the other hand, stationary objects such as the doctor a (30 of FIG. 6) hereinbefore described will be continuously wiped or cleaned by the spiral effect of the grooves. In this respect also, it will be appreciated that cleaning of the grooves themselves would be complicated except for a device which is employed in the practice of the invention and this device constitutes a pumping type Wiper (29 of FIG. 6) as shown here diagrammatically at w. The pumping type wiper is unique for wiping a grooved roll in that it does not penetrate the grooves. The wiper w is a unique simple structure that carries out its function at the oncoming side of the doctor so as to draw water at of the grooves and, if any is left on the land areas, the doctor may remove the same. In essence, the wiper is an axially continuous surface sheet or portion which extends from close proximity (there being presumed to be a slight water film) at the surface portion or land areas of the roll and the wiper w then presents a surface portion extending gradually away from such close proximity to the roll at such land areas so as to define at the off-running side of the wiper a gradually diverging pair of surfaces which automatically will create a pumping effect for driving the liquid out of the grooves. It will be appreciated that a wiper of this type has distinctly superior function in connection with spiral grooves, not only in that it is not required to penertate the grooves but also in that the nature of the spiral grooves will serve to continuously clean the wiper.

In many respects, the foregoing structures of the grooved rolls 13 and 22 are particularly useful even though the groove mouths 16, 25 may be rather substantial in size (e.g. up to 0.1 inch or more at the felt only nip N-d), and in fact, even to the extent of causing some marking at one of the web nips. In the preferred embodiment of the instant invention, however, marking is avoided by the use of very narrow groove openings 16, 26 of an axial dimension that is not greater than about 0.035 inch (and preferably about 1 of an inch). This axial dimension, as a maximum, has been found to be distinctly superior for use in the practice of the instant invention. It has been found that axial dimensions significantly greater than this do not give significantly better performance in any of the ordinary uses of the instant roll, whereas such larger axial-dimensions do have a tendency to cause web marking in most instances. In the manufacture and sale of grooved press rolls for the uses contemplated in the practice of the instant invention, it has been found particularly desirable to maintain the groove axial dimensions of 0.035 or less. Among other things, this has the advantage of avoiding any special instructions in connection with mill use by the grooved rolls, since such grooved rolls can be used at felt only presses, as well as web presses involving different felt weights and different quantities and types of webs. In fact, most recent work has indicated that a preferred maximum is about 0.020 inch with 0.1 inch lands. (Although a preferred range is 0.020 to 0.025 inch grooves with 0.080 to 0.100 inch lands.)

Within the limitations hereinbefore set forth, it will be understood that certain relationships between the groove and ridges in the felt-covered press roll eg 13 and 22 of a web press in a divided press may be so critical be cause of the felt 11 is adapted to carry away most of the water expressed from the web W-l and rewetting of the web is avoided in FIGURE 1 by guide means (i.e. 52e and again at 11c) separating the web and felt at the immediate orT-running side of a nip. In the case of nips such as the nip N-1 where the felt 11 cannot be separated from the web W1 immediately after the nip, however, the ratio of axial groove dimension 16 to axial land dimension 17 becomes important. Thus, in situations when it is not so important (e.g. for the roll 12) this ratio is at least about 1:1 and preferably at least about 1:2 to 1:3 (i.e. of an inch to about to 7 of an inch) for satisfactory removal of water from the web by the felt 42, which actually involves an open area in the range of 50% to about 33% and 33 /3 to 2025% or less. This latter range is the preferred open area, however; and it is the open area actually used on roll 12.

Extensive research has revealed that distinctly superior performance is obtained using a substantially smaller open area of not more than about 25% (e.g. not more than 3 inch grooves with inch lands). This is a significant difference between the rolls 13 and 22. This is true notwithstanding the fact that an essential aspect of the invention involves ease of reception of water into the grooves. The reason for the preferred open area upper limit of about 25% (and preferably 20% with 0.020 to 0.025 inch grooves and 0.80 to 0.1 inch lands) is that it has been found that this comparatively low open area does not significantly impede water removal from the web (via the felt) at the nip pressures used and at the small axial dimensions 27 used, while this reduced open area does carry out perhaps the second most important function of the invention and that is that it provides for considerable versatility in the use of the grooved roll of the invention. This function is that of minimizing rewetting of the expanding absorbent felt at the ofi-running side of the nip. Although this function greatly assists the dewatering operation in the web press nip (if a divided press is used) and reduces or minimizes the water load carried away by the felt from the web in the divided press, it must be appreciated that this function is also capable of effecting substantially all water removal (via a grooved roll at a web press nip) so as to replace a conventional suction roll web press, as indicated at the nip N-2 or N-3 shown in FIGURE 1.

In the nip N-2 of FIGURE 1 the roll 47 has the general structure of the roll 22 hereinbefore described, but in addition it will be appreciated that it is specifically cut with an open area of only about 16%, i.e., 0.020 grooves with 0.1 inch lands. The roll 47 thus operating with guide means 111) and 110 for maintaining the felt substantially tangential to the nip N-2 is capable of carrying out a dewatering function of its own and removing this water via its own saveall system 4712, even though the roll 47 is used as a part of a divided press system. It is important to note that this additional versatility is afforded by the use of the low open area just described.

For additional detail in connection with the nip N2, attention is directed -to FIGURE 8 showing that the felt 11 and Web W-1 are preferably maintained below the tangent line T-T for minimum contact with the grooved roll, here indicated at 42 (since the press of FIG. 8 is not identical to the press 47-48 at the nip N-2 in FIG. 1). In FIGURE 8, the roll 42 is comparable in structure to the rolls 47 and 22, with grooves 420 and lands 2212, a wiper system 49 comparable to that at 29 in FIGS. 6 and 7, a doctor 50 comparable to that at 30 in FIGS. 6 and 7A, and a saveall system 45a45c, showing in greater detail the saveall type 47h of FIG. 1 for a top grooved roll 47 in a web press W-Z.

In contrast, the nip N-l of the roll 12 does operate with a felt 52 that is separated therefrom substantially at the ofi-running side of the nip, so the roll 12 can carry out a substantial dewatering function using an open area of approximately 20%, i.e. 0.020 inch grooves with 0.080 inch lands. Because the roll 14 is necessarily wrapped to some extent by the off-running side of the felt 11, it will be appreciated that the felt 11 will in its own highly absorptive capacity tend to re-absorb a considerable amount of water in the grooves, but it will not completely 14 absorb all the water in the grooves of the roll 14. order to provide the roll 14 with capacity to retain water which is pressed into its grooves at the nip N-l, it would be advisable to employ smaller mouths on the grooves.

and deeper grooves, e.g., 0.01 inch grooves having a depth of approximately 0.2 inch.

It will be appreciated also that, should it be advised that the web should stay with the felt 52 in the particular press operation, then the relative groove and land structures in the press rolls 12 and 14 would be reversed.

areas and into the grooves, whereas at the lesser opposite pressures at the off-running side caused by the absorptive nature of the felt and the partial vacuum created there,

the water must travel not only out of the grooves but back toward the middle of the land areas. It has thus been found that the preferred structure of the roll 22 for this undesired reversal of water travel involves a ratio of grooves width 26 to land width 27 of a practical maximum of about 1:2 to a practial minimum of about 1:20 below which dewatering of the web and/or felt is unduly hampered (and preferably this involves an open area within the range of about 25% to about 10% Particularly using the combination of the foregoing groove-to-land ratio of 1:2 to 1:20, lands of substantially 0.05 to 0.15 inch width and-grooves of 0.01 to 0.035 inch width are preferred. Excellent results have been obtained using 0.025 iuch'grooves with 0.1 inch lands; whereas still better results have recently been obtained using 0.020 inch grooves with 0.1 inch lands, i.e. 16% open area.

Groove depths 28 at least sufiicient to carry the water load are used, and of course, these must be sufficient to carry out the function of venting which is essential to the practice of the invention. have demonstrated a distinct preference for groove depths of at least about 2 to 10 times the groove mouth width,

or at least about equal to the land width or at least about 0.1 inch, with maximum groove depth being defined primarily by practical considerations, although square or rounded groove bottoms not substantially deeper than about 4 inch are generally superior to other structures for the combination of strength, cleaning and manufacturing purposes.

It will be appreciated that the grooved rolls are in most instances designated with a G near the center thereof and anti-deflection pneumatic loading mounting means are designated symbolically also in most instances in the various views by the use of two-headed arrows within the circumference of the symbolical showing of the roll. Such anti-deflection mounting means are shown in US. Patent No. 2,648,122; 2,651,103; and 2,651,241. In addition, in my co-pending applications Serial No. 102,571, filed April 12, 1961, now US. Patent No. 3, 097,590 and Serial No. 154,801, filed November 24, 1961, now US. Patent No. 3,097,591, preferred embodiments of anti-deflection roll mounting means for such rolls are disclosed and the anti-deflection roll mounting means employed in the practice of the instant invention involve' the rubber sandwiches on a through shaft as shown in my application Serial No. 102,571 for the mounting of each of the rolls herein.

It will further be appreciated that in the usual initial press such as the press nip N1 (and in the usual initial transfer press), the loads are relatively low (often be cause a suction roll is used in one of these presses); but

The foregoing requirements grease? in the practice of the instant invention higher loads can be used and more dewatering can be accomplished mechanically accordingly. It will thus be appreciated that the nip N-1 can be operated at 200 to 300 pounds per lineal inch, if desired, and the subsequent nip N-2 can be operated at 350 to 400 pounds per lineal inch, if desired. The felt only press nip N6 would then be operated at still a greater pressure to accomplish the necessary dewatering, which would be some 50 pounds per lineal inch greater than the nip load at the nip N-Z. The felt only press nip N-7 would also be operated at approximately 50 pounds per lineal inch nip load greater than the nip load at the nip N-l in order to carry out its function of dewatering to compensate for the water picked up at the nip N-l.

One of the problems in web pressing previously discussed herein is avoidance of crushing of the web which is perhaps a poorly chosen but very meaningful Word of the artactually meaning incipient fracture of the web-caused by excessive, poorly directed water flow in the web at the nip. Thus, referring to FIGURE 4, it will be seen that at the oncoming side of the nip N4 the pressure P in-the porous belt 11 is nominal (i.e. about 15 p.s.i. abs); whereas at the middle (or cross machine center line) of the nip N-l the pressure P is at a maximum (usually at least as great at the nip load in p.l.i. or greater because the longitudinal dimension of maximum nip load is often less than one inch); and, of

course, at the off-running side of the nip N-l the expanding felt 11 tends to create a subatmospheric (or vacuum) pressure P (e.g. 2-5 p.s.i. abs.) depending to a great extent on the ability of the porous felt or belt 11 to receive ambient atmosphere (since the pressed web W1 is substantially non-porous in this condition).

Generally in crushing, P is so much greater than P that in the case of a substantal total water load entering the nip N-l there is created a flow of water in the web from P toward P and this results not only in the visible collection of water as a pool at the oncoming side of the nip but also in a web pro-duct which will have many small cross-machine cracks or incipient fractures that can be observed in the final product. The grooves 13c, however, being vented to ambient atmosphere afford the easiest water flow path (backward and forward) in the nip, so even though the pools of water may be evidenced in the present press nips, crushing of the web can be avoided, because there is an avoidance of undesirable water flow in the web itself.

Referring to FIG. 513, it will thus be seen that the maximum pressure P actually occurs only at the machine direction center-line M of each land area 22b (generally along the cross-machine center-line of the nip N-l) and the minimum or nominal pressure P is actually very closely adjacent thereto (along the cross-machine centerline of the nip N1) so that the net effect of pressure application at the nip N-3 may appear to be the same (or greater, depending upon the particular press position) nip load in p.l.i. (pounds per lineal inch) but the water flow from the moist web W-ll to the porous felt or belt 11 is essentially (non-crushing and) normal to the plane PP between the web W-I and the felt 11 (e.g. as shown in FIGURE A). There is no crushing flow of water in the web along the plane PP in the direction P P nor is there in the nip N-l of FIGURE 5C. The extremely small axial dimension 27 of the lands 22b, 22b (FIGURE 53) avoids any cross-machine crushing flow of water in the web in the direction P P Instead, in FIGURE 5B, there is presented a felt ll which has theoretically a low average pressure m-io 2 to readily receive water generally normally to the plane PP at the web-fe1t, interface, followed by flow of water 16 to a limited extent only within the felt I1 and for the limited dimension 27 /2 in the direction P P This affords an advantage of extremely high press nip loads (in p.l.i.), when desired, without crushing.

It should also be noted that, even assuming that, in FIGURE 5B, P is equal to such desired high nip loads as 100, 200, 300 or even 450 p.l.i. (although P in p.s.i. will probably be much higher often because the longitudinal dimension of maximum nip pressure P is usually less than one inch), the driving force against the water is P P which is usually in the range of several hundred psi. The time this driving force is applied is very brief (i.e. for a machine speed of 2000 feet per minute and an oncoming nip side of perhaps one-half inch, being approximately 3 10' sec.) but the driving force is so great and the maximum water travel path 27 /2 so small that substantially all of the water is almost instantly driven into the deep grooves 22c, with substantial avoidance of a web crushing pressure gradient in the nip plane PP either longitudinally or in the cross-machine direction. In particular, the very narrow (axially) lands 13b and 221; between narrow (but appropriately large) grooves and 220 make this physical phenomenon possible. Hence land (axial) widths, particularly for higher speed machines, in the neighborhood of 0.05 to 0.15 (and preferably 0.08 to 0.1) are important.

The groove dimensions are also important in that 0.025 may be ideal for a given press whereas a reduction to 0.02 for the width 26 (FIG. 5B) in the same press has been found to produce a distinct reduction (or substantial elimination) of evidence of marking in the certain Webs thereby demonstrating the criticality of even superficially very small dimensional changes in this aspect of the structure.

Still another extremely important aspect of groove structure is the cross-sectional volume, which has already been expressed in terms of a mouth width (26) of x as a practical minimum of twice the square of the mouth width (i.e. at least 2x and preferably four to five times such square (i.e. 4x to 5x Since the third dimension of the volume of the grooves, in the longitudinal or machine direction, is infinite for practical purposes; the volume is here expressed in terms of a value defined on the basis of the other two dimensions, which actually express a cross sectional area that is numerically represenative of the volume. In machines which operate very slowly, such that water actually flows in such grooves away from the nip involved (perhaps even at greater speeds than the grooved roll peripheral speed) still greater volumes of 16x to 20x may be highly desirable. This volume is not necessarily so much for merely the desired capacity to receive water but more for the necessary ability to vent to the atmosphere and maintain P (FIG. 5C) at substantially ambient atmospheric pressure of 15 p.s.i. abs. In pulp making machines, wherein the speeds are relatively slow and the water loads relatively high the grooves may actually function very satisfactorily as flow troughs using the dimensions of 0.02 to 0.025 inch mouth 26 with a normal machine taper (e.g. 7%) to a depth 28 of only 0.06 inch, i.e., a cross-sectional area of 2 to 3x (even though the larger volumes suggested are preferred). It is important to consider the groove volumes (i.e. which must be volumes to function to receive water, although best expressed numerically on the basis of the aforesaid cross-sectional areas) on the basis of the groove mouth width "x because shallow tapered groovesmay be incapable of the necessary venting function and/ or the necessary ability to resist the tendency for the felt to reabsorb all of the water in the grooves at the off-running side of the press nip.

The groove mouth width 26 has still another very important function, often expressed in terms of open area, and this pertains to overall resistance to water return from the grooves to the (subatmospheric) felt at the offrunning side of the nip. Again, using the previously described operating conditions, it will be appreciated that, during the very brief period of approximately 3 l0' sec. in which the felt expands at the off-running side of the nip (cross-machine) center-line, the driving force of P, minus P or 10 to 12 psi. tending to return water from the grooves to the absorbent felt is comparatively much less than the several hundred p.s.i. driving force pushing water into the grooves at the oncoming side' (during an equal time interval). The term P is used herein to indicate ambient atmospheric or zero gauge pressure, and the term P, is here used to indicate a partial vacuum or perhaps 3 to psi. absolute. Additional unfavorable factors include the effect of centrifugal force and the effect of perhaps a longer time interval (since it is difficult to separate the felt from the grooved roll surface at the very instant that nip pressure is relieved); but all of these unfavorable factors are more than counteracted by (a) the very great differences in actual driving forces, (b) the reasonably rapid removal of the felt from the grooved roll surface, and (c) the water travel path, since the water must travel (1) first generally normally to the felt plane (toward the groove mouth) for (2) a rather substantial distance (particularly in the case of the water at the bottom of deeper grooves) past closely adjacent groove walls tending to resist water movement both by (3) frictional drag and (4) molecular (or capillary-like) attraction between the water and the groove wall material and then through (5) a right angle turn for (6) still another substantial distance 27 /2 (FIGURE SE) to the center-line of the land area. Water removal is thus effected at conventional higher machine speeds and the lower open areas here specified simply because the offrunning time interval is wholly insufficient to permit the felt to withdraw all of the water from the groovesor even, for that matter, to permit creation of equilibrium or balanced water conditions vis-a-vis the felt and grooves.

Depending upon the machine speed, the time interval for actual felt expansion (i.e. complete pressure removal) may range from about to about 10" second; but the time interval for felt travel in contact with the grooved roll surface of the maximum pressure (P cross machine load line may possibly involve as much as 10 second, although it is more in the neighborhood of 10 or 10- in ideal press nip arrangements such as those of FIGS. 6 and 8 hereof. Although certain aspects of the phenomena involved, in driving water into these fine groove (e.g. 0.020-0025 inch grooves) under driving forces of 100 to 500 p.l.i. in time intervals of 10* to 10 seconds and then minimizing withdrawal of water therefrom at the lower off-running driving forces of 10- 12 psi. in comparable periods of times cannot be fully understood; it is known that within the method parameters herein set forth water removal from the web-felt system is efiecting in such grooves, without any apparent web damage.

At slower operating conditions using the same structures, even if equilibrium conditions were reached, the grooves must hold and carry off substantial quantities of water. And at even'slower conditions such as were indicated as a possibility with a pulp machine, the comparatively larger land areas afford the necessary nip pressure application whereas the comparatively (axially) smaller grooves afiord vented, free flow of water away from the nip and out of the system into conventional receptacles. In any case, water removal is thus effected.

It will thus be seen shallow and/or sharply tapered grooves, having a semi-circular or a triangular crosssectional area which is functionally significantly below about twice the square of the groove mouth width (i.e. 2x are either incapable of satisfactory venting, satisfactory resistance of return of water to the absorbent, felt at the off-running side of the nip, or both. The suggested minimum of 2x is practical as well as functional, since it is conceivable that certain principles of the invention could be followed, for example, using shallow grooves 18 having the general" cross-section of perhaps an equilateral triangle (i.e. /ax with a relatively deep but very narrow and hence small volume slot of only perhaps 0.002 inch width extending radially inwardly from the' apex of such triangle; but such slot would have to have some functional volume because this would constitute es-Y sentially the only volume of water not reabsorbed by the felt from such shallow grooves in normal operation, andagain in slow operation the slot would still require some Volume to afford the required venting function (and to this end continuous cleaning to keep the slot functional would be dificult or impractical). The grooves have already been described as requiring substantial depth to accommodate these essential functions.

Occasional cross-machine slots on the lands (and/or conduits beneath the land surfaces) interconnecting the generally circumferential grooves would not be precluded by the basic principles of the invention, but such struc-' tures are not preferred primarily because whatever use-" ful function they might have would ordinarily be impaired by practical considerations relative to maintaining such structures clean. In ordinary operation, for example, the cross-machine slots on the lands would probably iill up quickly and unless continuously cleaned by additional auxiliary equipment such as brushes, etc. func--' tionally continuously cylindrical lands would result. In any event, whatever type of groove structure attempted (other than the hereinbefore described substantially circumferential structure) would be subject to the same also all so-called felt of different weights, weaves and openness, including reinforced felts (substantialy incompressible), porous fabrics and similar porous belts which may be composite, integral or separable porous elements and/ or combinations of compressible felts with relatively incompressible plastic or metal forming wires, etc. wrapping the grooved rolls.

It will be noted that in FIGURE 5C the roll 22 is indicated as being provided with a rubber cover, whereas the opposing press roll need not also be provided with a rubber cover but may be optionally. In general, in press sections, it is preferable to have one of the rolls capable of yielding slightly so as to avoid serious damage to the machinery in the case of accidents and this is usually done by providing a solid elastomer type of cover for one of the rolls. In the practice of the instant invention this solid elastomer type of cover may be used for one or both of the grooved rolls defining felt only press nips or the press nips which involve two felts. There are some advantages to the use of a stainless steel clad roll with grooves cut therein and one of these positions, in that the stainless steel clad roll will have greater durability, but in general only one of such rolls forming a press couple would be stainless steel clad and the other would be clad wtih a solid elastomer for the reasons just described.

Referring briefly to FIGURES 11 and 10, it will be seen that these views show in diagrammatic elevation three roll divided passages which may be substituted for the press 20 at the nip N-3 in FIGURE 1 or may be employed subsequent thereto as still another press for dewatering the web. In FIGURE 11, the webs'indicated as W-201 and it comes into the nip N- on the felt 124 and separates from the felt 124 to ride briefly upwardly on the uprunning side of the plane Microrok or granite roll 121. This minimizes the overall contact time (e.g. in the neighborhood of 10* seconds) between the web W400 and the felt 124 while the felt is still in contact with the grooved roll 122 (and while the reabsorption process hereinbefore described may be taking place to a limited extent). It will be noted that the intermediate grooved roll 122 is provided with doctors 127 and 127a and wipers 126 and 126a in savealls 123 and 12311 at both the downrunning and the uprunning sides thereof for the reasons that each of such sides of the roll 122. are actually approaching a grooved press nip. The uprunning side approaches the web nip N-120. and the down-running side approaches the felt only nip N- 120A. The bottom roll 123 cooperating as a groove roll 122 to define the felt only nip NANA functions in the manner hereinbefore described in connection with FIG- URE 8 to afford minimum contact between the felt 124 and the grooved roll 122, except at the region of maximum nip load. Doctors 123a and 12312 and the saveall 123s are conventional for the roll 123.

In FIGURE 10, a comparable arrangement is shown using three rolls to define an upper web press nip N430 and a lower felt only press nip N130A, and elements corresponding in structure and function to those shown in FIGURE 11 are designated in FIGURE 12 in the 130 series as contrasted to the 120 series of reference numerals used in FIGURE II. The essential difference in FIG- URE is that the bottom roll 133 is also a grooved roll, so that the felt 134 is subjected to the action of grooved rolls 132 and 133 at opposite sides thereof in the felt only nip N-130A. A difference in operation is contemplated between the devices 120 and 130 in that in the device of 130, the intermediate grooved roll 132 may readily carry a substantial amount of water from the web press nip N430 downwardly into the felt only press nip N130A (-and this would occur if the press 130 is operated at sufficiently slow operating speed), which phenomenon is not generally contemplated in the operation of the press 120. This is because the bottom grooved roll 133 can actually carry away substantially all of the water that must be removed from the system of the press 130, whereas the bottom roll 123 is not grooved in the system 120.

It will be noted further that the operation of the wiper 133a shown in FIGURE 10 is facilitated by the use of an oncoming doctor 133d to wipe the lands dry and permit the pumping type wiper 133a to have better functional engagement with the lands of the grooved roll 133 to assist in its pumping function.

4 Attention is also directed to the fact that the bottomed grooved roll 133 has a rotary brush 133x that is mounted for cleaning the downrunning side of the grooved roll 133 by, continuous high speed rotation of such brush having flexible resilient fingers or tendrils, or typical brush bristles which possess the necessary flexibility to avoid breaking or damage even in the case of helical grooves in the roll 133, but which do provide a positive type of cleaning action that is more drastic than that effected by the pumping'type wiper 133a and which may be useful in many machines here employed. It has been pointed out that the pumping type wiper w or 133a as indicated in FIGURE 10 is unique in that it may clean relatively fine spinal grooving essentially by pumping; and this is an important advantage of the invention. On the other hand, in certain particular uses, a more complicated type of grooving may be employed on the surface of a given grooved roll used in the practice of the instant invention. In general, the simple generally circumferential grooves (With a slight helix) have already been described as being preferred for use in the practice of the invention and grooves of this type are distinctly superior for a number of reasons. Nevertheless, there may be instances when it might be desirable to use other grooved structures and such other grooved structures are indicated in FIGURE 9, in top plan view of a fragmentary, small portion of a roll surface, with the views 9A, 9B and 9C indicating fragmentary sections taken in these structures.

For example, in the view of FIGURE 9, it will be seen that the roll surface indicated generally by the reference numeral 2th) is provided with a first plurality of helical grooves 201a, 2012),231C, etc., which are shown as having a helix angle substantially greater than that previously described in connection with the preferred generally circumferentially aligned grooves and ridges. Likewise, the structure of the roll 2% is provided with a second set of generally helical grooves indicated in part at 202a, 202b and 2020 which have a comparable helix angle to the grooves of the 201 series, but are reversed in direction so as to intersect the grooves of the 201 series thereby obtaining generally diamond-shaped land areas indicated at 203a and 26312. It will be appreciated that the maximum axial dimension of such land areas is represented in FIGURE as extending from a groove intersection R to a groove intersection S shown in plan view in FIG- URE 9. The groove width of x compared to the land axial dimension y shown in FIGURE 90 is still within the scope of the instant invention, being on the average about a ratio of x:y of 1:6 or 1:7, and the groove width x that is adapted for use in a web press in the practice of the instant invention will still be within the groove width range hereinbefore specified (i.e. about 0.005 to about 0.035 inch). The land width y in FIGURE 9C is, of course, closer to the upper limit of about 0.25 inch hereinbefore specified for the land Width, in order to minimize cross-machine flow in the plane of the web, hereindicated diagrammatically at W-9 and thus minimize cross-machine crushing fiow. The grooves of the intersections R and S are thus sufiiciently close together to avoid the necessary venting to ambient atmosphere at the underside of the felt F-9 for the purposes already described herein.

In FEGURE 913, it will be seen that the generally paral lcl (although slowly helical) grooves 20111 and 2010 have a more narrow land width yB therebetween in the section shown in FIGURE 93, so that crushing flow in the web is avoided in the direction of the section line IXB- IXB for the reasons hereinbefore described. In the section of FIGURE 9A, it will further be seen that a still more narrow land area yA even in the cross-machine direction of the section line IXAIXA is afforded between the grooves 202a and 20112, as there shown. It will thus be seen that the overall average land width y is within the parameters already set forth, and the grooves of the 201 and 202 series may thus function in the manner hereinbefore set forth, i.e. the overall open area does not exceed 33 /s% and/or the overall average land to groove ratio is 2:1 or more in the cross-machine direction. The previously described pumping wiper may also be used to remove Water from the grooves of this type also, but a rotary brush such as the brush 133x in FIG- URE 10 would also be preferred for use in conjunction with the pumping type wiper in order to maintain the grooves in a relatively clean condition for best operation.

lso, it will be noted that the roll itself is provided with a rubber cover 200a on a ductile iron shell 200x; and in forming the surface structure indicated in FIGURE 9, it is normally necessary to run the rubber covered roller 200 through a first cutting operation to cut, for example, the helical grooves of the 201 series in one direction and then process the roll 2% a second time to cut the helical grooves of the 202 series in the opposite direction.

The grooves of the 201 and 202 series of FIGURE 9 are actually vented peripherally before and after any nip and on the underside of the felt indicated diagrammatically at F9 at such nip and they are sufficiently narrow to carry out many of the other functions hereinbefore described. Having such a large heliv angle, however, these grooves 201 and 202 are not vented to ambient atmosphere through the shortest distance, as would be the case in the previously described generally circumferential grooves.

Also, assuming that the dimensions yB between the generally parallel helical grooves 201k and 2010 is approximately 0.1 inch and the grooves are 0.020 inch, it will be appreciated that this would (in the absence of the.

21 other set of helical grooves 202) form a basis for an open area of 16%; but the inclusion of the other set of grooves 202 increases the open area to at least about 20%, using grooves 202 of the same size as the grooves 201. Actually, the open area in patterns such as that of FIGURES 9 and 10 may be as much as about 33%, particularly if the machine is to be operated relatively slowly and the grooves are themselves out with substantial volume so that they may function as Water troughs. In such instances, land areas of approximately /3 of the total area may effect the desired pressing and the initial open area for grooves receiving water flowing away from the nip may be useful. Likewise, the land areas of maximum dimension, such as the land area y of FIGURE 9C may be as much as twice the previous suggested minimum of 0.15 inch, or such land area y of FIGURE 9C may be as much as 0.3 inch in its maximum dimension. It will be appreciated that this maximum happens to be in only one particular direction (i.e. exactly the cross-machine direction) whereas the land sizes here are so small compared to the overall nip size that in a relatively slowly operating machine, the escape routes for the water to the grooves 201 or 202 may well be much shorter, as indicated in FIG- URES 9A and 9B, and satisfactory venting of the upper side of the felt W-9 is readily accomplished to afford the function of water troughs for the groove system here described.

It wifl be appreciated that if a cross channel (not shown) is used it will have a tendency to fill up with fiber, clay, dirt or the like during operation, particularly in a felt only press nip operating against the other peripheral side of the felt, for this reason a brush such as the brush device 133x of FIGURE 10 or a similar device having bristles or similar flexible resilient elements capable of reaching into the grooves without being broken or damaged may readily be used to continuously clean such cross channels or cross grooves 201, although this involves too slow an auxiliary equipment and perhaps additional wear on the surface of the grooved roll, if the grooved roll surface is provided by a rubber cover 200a. Of course, if a metal or stainless steel type cover is employed, the advantages of the configurations shown in FIGURE 9 may be afforded and the use of a rotary brush 133x with bristles will actually result in substantially no damage or wear to such metal covers.

Again, the open area involved is preferably maintained at less than 33% (and, of course, preferably in the neighborhood of 25% or less for the reasons already described), but the groove 201 and land 203 configuration may be varied to some extent to suit particular needs and to this extent cross channels (not shown) may have useful function, in spite of the probable necessity for additional auxiliary equipment such as the rotary brush 133x for maintaining such cross channels in clean operating condition.

In further considering the nature of the flow of water from the web into the felt in general in the practice of the instant invention, it will be appreciated that the underside of the felt, i.e. the side of the felt not contacting the paper web is vented at a plurality of very closely spaced and very narrow vents. This results in the important directing of the flow of water generally normal to the plane of the web in the nip, which is the plane common to both rolls at the nip. It will thus be appreciated that the instant invention also involves a concept of dewatering a traveling paper web generally in the plane of a tangent to a pair of nipdefining rolls, which comprises squeezing the web against a porous felt or belt along a line in such tangent plane generally normal to the direction of web travel (which is considered the nip load line) to drive water in the web away from said line, and venting the underside of the porous felt to ambient atmosphere so as to substantially drive the water from the web away from said line into said felt along a second plane passing through the line and generally perpendicular to the aforesaid tangent plane, and the invention of course, provides for venting to the ambient atmosphere by the use of very narrow openings of generally axial dimensions of 0.005 to 0.035 inch and closely axially spaced by substantially 0.050 to 0.15 inch (or preferably within the range or aver age of l to 6 or 7 times the groove width), whereby the water flow in the web in such tangent plane is less than a crushing fiow rate. In other Words, the water flow either forward or backward in the tangent plane of the web is minimized and reduced to less than a crushing flow by the venting tendency which tends to align the flow of water in a direction that is generally perpendi ular to the plane of the web in the tangent position. In addition, however, the very narrow land areas of preferably substantially 0.050 to 0.15 or 0.25 inch are such that cross-machine flow along the nip load line in the web itself is minimized or so nominal that no crushing flow rate is achieved.

Expressed in other terms, the instant invention comprises a method of dewatering a paper web traveling generally in a plane, but comprises squeezing the web against a porous belt along a line in the travel plane of the web but generally normal to the direction of travel, and venting the side of the belt not engaging the Web to ambient atmosphere at a plurality of very narrow 0.005 to 0.035

inch areas closely spaced apart by substantially 0.05 to' 0.15 inch in a second plane generally normal to the web' travel plane and passing through said line, whereby flow of water in and from the web into said belt is substantially in said second plane and is substantially less than a crushing flow rate.

An additional aspect of the invention is shown (essentially diagrammatically) at W12 on the grooved roll 14; and the overall structure is shown in greater detail in FIG- URE 12A of our copending application Serial No. 305,-

carrying both the wiper W-12 and the immediate olfrunning doctor d is closed at the sides of the machine and a vacuum pump V of conventional construction is used to create subatmospheric pressure within the chamber thus defined for assisting primarily in rapid water removal'and in assisting the wiper W-12 in withdrawing water from the grooves. In particular, the aspects of said FIGURE 12A previously described are included herein by reference.

I claim as my invention:

1. A generally cylindrical press roll shell adapted to be mounted for rotation about its centroidal axis and to present to a pressure nip a peripheral rotary surface portion,

said surface portion having alternating generally circumferentially aligned grooves and ridges, said grooves hav- 6 ing an axial dimension at the roll periphery of 0.005 to 0.035 inch and'extending radially inwardly to impart to the cross sectional area of each said groove a value substantially equal to at least twice the square of said groove axial dimension, said ridges each presenting a generally cylindrical outer peripheral land area having an axial dimension of 0.05 to 0.25 inch that is substantially 2 to 20 times said axial groove dimension, as an average along an axial line on the roll periphery, thereby presenting a rotary surface portion with an average effective open area of not more than substantially 33 /3 2. A generally cylindrical press roll shell adapted to be mounted for rotation about its centroidal axis and to present to a pressure nip a peripheral rotary surface pbrtion, said surface portion having alternating generally circumferentially aligned grooves and ridges, said grooves having an axial dimension at the roll periphery of 0.005 to 0.035 inch and extending radially inwardly to impart to the cross sectional area of each said groove a value substantially equal to 4 to 5 times the square of said groove axial dimension, said ridges each presenting a generally cylindrical outer peripheral land area having an axial dimension of 0.05 to 0.15 inch that is 2 to 20 times the axial groove dimension.

3. A generally cylindrical press roll shell adapted to be mounted for rotation about its centroidal axis and to present to a pressure nip a peripheral rotary surface portion, said surface portion having alternating generally circumferentially aligned grooves and ridges, said grooves having an axial dimension along an axial line on the roll periphery of 0.020 to 0.025 inch and extending generally inwardly from said line to impart to each said groove in a plane common to the line and the roll axis the cross sectional area of a value substantially equal to 2 to 5 times the square of said groove axial dimension, said ridges presenting a generally clindrical outer peripheral land area having an average axial dimension in said plane of 0.08 to 0.1. inch.

4. A generally cylindrical press roll shell adapted to be mounted for rotation about its centroidal axis and to present to a pressure nip a peripheral rotary surface portion, said surface portion having alternating generally circumferentially aligned grooves and ridges, said grooves having an axial dimension at the roll periphery of 0.005 to 0.035 inch and extending generally radially and parallelly inwardly for at least about 0.05 inch between side walls that are axially spaced at least as much as said groove axial dimension at the roll periphery, said ridges each pre-.

senting a generally cylindrical outer peripheral land area having an axial dimension of 0.05 to 0.25 inch that is 2 to 20 times the axial groove dimension at the roll periphery.

- 5. A generally cylindrical press roll shell adapted to be mounted for rotation about its centroidal axis and to present to a pressure nip a peripheral rotary surface portion, said surface portion having alternating generally circumferentially aligned grooves and ridges, said grooves having an axial dimension at the roll periphery of 0.005 to 0.035 inch and extending generally radially and parallelly inwardly for at least about 0.05 inch between side Walls that are axially spaced at least as much as said groove axial dimension at the roll periphery, said ridges presenting a multiplicity of generally cylindrical outer peripheral land areas in a total axial dimension averaging 3 to 20 times the total axial groove dimensions at the roll periphery, said grooves defining a plurality of continuous spirals on the periphery of said roll.

6. The roll shell of claim 1 wherein the grooves are aligned in spirals which are aligned to intersect from time to time on the roll periphery and at any given axial line taken along the roll periphery the ratio of groove width to land area with ranges from 1 to 7.

7. A generally cylindrical press roll shell adapted to be mounted for rotation about its centroidal axis and to present to a pressure nip a peripheral rotary surface portion, said surface portion having alternating generally circumferentially aligned grooves and ridges, said grooves having an axial dimension at the roll periphery of substantially 0.02 to 0.025 inch and extending radially inwardly substantially A3 inch between substantially radial Walls, said grooves defining a continuous spiral on the periphery of said roll, and said ridges each presenting a generally cylindrical outer peripheral land area having an axial dimension of substantially 0.1 inch.

8. The roll shell of claim 5 wherein said plurality of continuously spirally aligned grooves are aligned to intersect from time to time and at any given axial line taken along the roll periphery the ratio of groove width to land area ranges from 1 to 7.

9. In a paper machine press section, in combination, a looped traveling moist felt, a first press roll, a second press roll engaging the felt defining with said first press roll a press nip for receiving the felt, at least one of said press rolls having a generally cylindrical press roll shell adapted to be mounted for rotation about its centroidal axis and to present a peripheral rotary surface portion thereof against the felt, said surface portion having alternating generally circumferentially aligned grooves and ridges, said grooves having a narrow axial dimension at the roll periphery for receiving water pressed from the Web and felt but also tending to resist flow of Water out of the grooves, said ridges each presenting a generally cylindrical outer peripheral land area having an axial dimension that is 2 to 20 times the axial groove dimension at the roll periphery, the grooves having an axial dimension at the roll periphery of 0.005 to 0.035 inch and extending radially inwardly to impart to the cross-sectional area of each groove a value substantially equal to at least twice the square of the aforesaid groove axial dimension.

10. The paper press section defined in claim 9 wherein the grooves are aligned in spirals which are aligned to intersect from time to time on the roll periphery, thereby presenting a rotary surface portion with an average etlective open area of not more than substantially 33 /3 11. The paper press section defined in claim 9 wherein the grooves are aligned in spirals which are aligned to intersect from time to time on the roll periphery and at any given axial line taken along the roll periphery, the ratio of groove width to land area width ranges from 1 to 7.

References Cited by the Examiner UNITED STATES PATENTS 1,321,956 11/19 Wagner 100-112 1,483,562 2/24 Wagner 162-358 1,517,036 1l/24 Wagner 29-121 1,520,489 12/24 Wagner 29-121 1,552,098 9/25 Wagner 29-121 1,905,911 4/33 Kellett 162-360 2,694,348 11/54 Beachler 162-359 2,732,772 1/56 Hornbostel 162-3 2,858,747 11/58 Wagner 162-361 2,869,437 1/59 Hornbostel et al. 162-360 FOREIGN PATENTS 733,105 7/32 France.

399,113 9/ 33 Great Britain.

680,349 2/ 40 Germany.

547,936 9/42 Great Britain. 1,005,719 1/52 France.

DONALL H. SYLVESTER, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,198,697 August 3, 1965 Edgar J, Justus It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, lines 12 and 13, after "machines. insert the following paragraph:

This is a continuation-in-part of my applications Serial Nos. 214,589, filed August 3, 1962; 258,391, filed February 14, 1963; 302,421, 302,422, 302,423, 302,270, 302,371, all filed August 15, 1963; 305,713, filed August 30, 1963; 305,992, filed September 3, 1963; and 316,602, filed October 16, 1963 and now abandoned. These disclosures are incorporated herein by reference to show numerous different embodiments in which the roll shells of my invention are used and the fundamental principles and concepts are demonstrated.

Signed and sealed this 14th day of June 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A GENERALLY CYLINDRICAL APRESS ROLL SHELL ADAPTED TO BE MOUNTED FOR ROTATION ABOUT ITS CENTROIDAL AXIS AND TO PRESENT TO A LPRESSURE NIP A PERIPHERAL ROTARY SURFACE PORTION, SAID SURFACE PORTION HAVING ALTERNATING GENERALLY CIRCUMFERENTIALLY ALIGNED GROOVES AND RIDGES, SAID GROOVES HAVING AN AXIAL DIMENSION AT THE ROLL PERIPHERY OF 0.005 TO 0.035 INCH AND EXTENDING RADIALLY INWARDLY TO IMPART TO THE CROSS SECTIONAL AREA OF EACH SAID GROOVE A VALUE SUBSTANTIALLY EQUAL TO AT LEAST TWICE THE SQUARE OF SAID GROOVE AXIAL DIMENSION, SAID RIDGES EACH PRESENTING A GENERALLY CYLINDRICAL OUTER PERIPHERAL LAND AREA HAVING AN AXIAL DIMENSION OF 0.05 TO 0.25 INCH THAT IS SUBSTANTIALLY 2 TO 20 TIMES SAID AXIAL GROOVE DIMENSION, AS AN AVERAGE ALONG AN AXIAL LNE ON THE ROLL PERIPHERY, THEREBY PRESENTING A ROTARY SURFACE PORTION WITH AN AVERAGE EFFECTIVE OPEN AREA OF NOT MORE THAN SUBSTANTIALLY 33 1/3%. 